1. Field of the Invention
The invention relates, in general, to rack ovens useful for baking or heating food products and, more particularly, to commercial rack ovens such as those used in the bakery industry.
2. Description of the Related Art
Commercial rack ovens typically include a baking chamber which is sized to receive a rack having multiple shelves containing food products to be baked or roasted; a power driven, rotating mechanism to rotate the food product as they are being baked or roasted; a combustion system including one or more fuel-fed burners with a heat exchanger; an exhaust system with a blower to eliminate the combustion gases; and a circulating system for directing hot air across the food products in the baking chamber to provide a rapid distribution of hot air over the food products. Conventional rack ovens of the type for baking bread generally include a steam generator for the introduction of steam into the oven.
A particular disadvantage of such ovens is the combustion/exhaust system used. There are several main types of combustion/exhaust systems presently used in the manufacture of rack ovens. In one system, air for the combustion mixture is drawn into the system by the action of the flowing gas under pressure. Without any additional means for moving the combustion gases, it is critical that the system employ proper fluing to eliminate the combustion gases. Another system employs an external electrically powered fan which drives air into the combustion system. In this system, ignition of the gas/air mixture is quite often difficult to achieve. Furthermore, as the system accumulates dirt over a period of time, less air is forced into the system while the same amount of gas is being supplied. This causes the gas/air ratio to become progressively richer until delayed combustion occurs resulting in an explosion (commonly known as “puffs”). These explosions are not only hazardous to workers, but can be very destructive to the equipment.
Another combustion/exhaust system is disclosed in U.S. Pat. No. 5,617,839. The heat exchanger uses a combustion chamber with a plurality of in-shot burners, each projecting into one of a first set of horizontally arranged heat exchange tubes. These tubes terminate in a first gas-collection duct or plenum, which feeds the hot combustion gases into a second set of horizontally arranged heat exchange tubes. The second set of tubes terminate in a second gas-collection duct. After the combustion gases travel through a series of such sets of horizontally arranged heat exchange tubes and gas-collection ducts, the combustion gases are expelled through a flue using an arrangement of a “T” exhaust duct, a nozzle and a ventor fan powered by an electric motor.
Among other problems, such a combustion/exhaust system requires electric power and use of a fan to create a power assisted draft. Further, such a system is complex, costly to manufacture and less reliable than desired. In addition, the heating of the several sets of heat exchange tubes is not uniform, which causes stress in the heat exchanger materials and an increased chance for failure.
In addition to the above combustion/exhaust system problems, many commercially available rack ovens have other disadvantages.